External Heater Question



  • I would like to use external heaters to heat up the print bed, then when the required temperature is reached, a signal will be sent to Duet Wifi to start print job.
    Where should I send this "signal" to?
    How should I modify the config or any other files to accommodate for that?



  • @pinkmaro May I ask why you don't want the Duet to control the external heater?



  • @deckingman we have a 2400W external heater



  • @pinkmaro you could control it anyway using the right SSR for that power.



  • Do you want to control the heater on/off from the board as well? Your best bet may be to use a thermocouple or thermistor for feedback. You could use a heater output pin to switch the heating element on/off as well if you need that functionality.

    This is how most people set up mains powered heated beds. Use a heater output to control a SSR which is doing the switching on the AC mains.



  • @pinkmaro said in External Heater Question:

    @deckingman we have a 2400W external heater

    As other have already said, you can use an SSR (Solid state relay) to control the bed via the duet board. Apart from simplicity, you'll then have the advantage of being able to use the Duet to tune the PID parameters and during printing the firmware will also then give you protection against under or over temperature excursions and take appropriate actions which would be difficult with a simple digital input.



  • Sorry if this is a really silly question, if I follow to use SSR, will the duet automatically know when my bed has reached the required temperature?
    If no, how do I notify the duet?
    I will be using K type thermocouple.

    I'm not good at all technically, and my question might sound really odd. But thank you all for being patient and responsive!



  • @pinkmaro said in External Heater Question:

    Sorry if this is a really silly question, if I follow to use SSR, will the duet automatically know when my bed has reached the required temperature?
    If no, how do I notify the duet?
    I will be using K type thermocouple.

    I'm not good at all technically, and my question might sound really odd. But thank you all for being patient and responsive!

    Yes. But to use a thermocouple, you will need to purchase an add on daughter board. You don't need an add on daughter board to use a "standard" NTK thermistor which are more than accurate enough for bed heater.

    An SSR works like a relay - in fact that's what it stands for "Solid State Relay". So you connect the low voltage side to the duet and the high voltage switched output goes to the heater. So the firmware monitors the temperature from the thermocouple or whatever sensor you choose to use, then switches the output of the board for the heater accordingly. This in turn switches the SSR which supplies power to the heater.

    Does that help?



  • Yes, I think it does, thank you!!! ^^ Looks I have a lot of reading to do to understand all the things about 3d printing. 😅 Will try out and come back if I have more questions.



  • @pinkmaro said in External Heater Question:

    ...................Looks I have a lot of reading to do to understand all the things about 3d printing. 😅 Will try out and come back if I have more questions.

    If you haven't already discovered it, this is a good place to start https://duet3d.dozuki.com/

    You find additional links to most things - this for example https://duet3d.dozuki.com/Wiki/Choosing_a_bed_heater - which will lead you to https://duet3d.dozuki.com/Wiki/Choosing_a_bed_heater#Section_Mains_voltage_AC_bed_heater etc....



  • After checking back with my dad, he wants to do it such that we will connect the bed to an endstop. We will then manually switch on the heaters and when the temperature has been achieved, we will trigger with an "on/off" to the endstop. Is there a specific Mcode/Gcode that I can use in my gcode to detect this signal on the endstop and inform the duet to start print job?



  • @pinkmaro Seems a little silly to not just use a thermistor since it's designed to monitor and wait for a temperature to be achieved before starting a print.

    But, I guess you could use the filament runout sensor configured as a simple switch. It would basically wait until filament is present and pressing the switch before proceeding with the print.

    https://duet3d.dozuki.com/Wiki/Connecting_and_configuring_filament-out_sensors


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